Interrelation of Inorganic Phosphorus Fractions and Sorghum‐Available Phosphorus in Calcareous Soils of Southern Khorasan

The objectives of this research were to determine inorganic phosphorus (P) fractions in calcareous soils of southern Khorasan and find their relationship with sorghum‐available P. Eighty soil samples were obtained and analyzed for some physical and chemical characteristics, among them 24 samples that varied in plant‐available P and soil properties were used for soil testing. From 24, 8 samples were selected for P fractionation as well. Five extraction procedures were used for soil testing. Results indicate that the extracted plant‐available P by the Olsen et al. (1954 Olsen, S. R., Cole, C. V., Watanabe, F. S. and Dean, L. A. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate (USDA Circ. 939), Washington, D.C.: U.S. Government Printing Office.  [Google Scholar]) and Paauw (1971 Paauw, F. V. 1971. An effective water extraction method for the determination of plant available phosphorus.. Plant and Soil, 34: 497–481.  [Google Scholar]) methods show the greatest correlation coefficients with plant P uptake and sorghum dry matter. The sequential inorganic P extraction analyzing indicated that the abundance of various inorganic fractions was in the order Ca₁₀‐P > Al‐P > Ca₈‐P > Ca₂‐P > Oc‐P > Fe‐P. The results also indicate Olsen P correlates positively and significantly with Ca₂‐P and Fe‐P fractions and positively but not significantly with the Al‐P fraction.     

Dynamics of Forms of Inorganic Phosphorus in Soil under Coffee Plants as a Function of Successive Annual Additions of the Nutrient

Phosphorus (P) dynamics and availability in soils are influenced by P fertilization. This paper aimed to evaluate inorganic P fractions bonded to calcium (Ca), iron (Fe), and aluminum (Al), associating them with soil mineralogy. The experiment was carried out using an acidic kaolinitic–oxidic soil, located in an irrigated area cultivated with coffee plants (Coffee arabica L.), submitted to successive annual fertilizations with triple superphosphate doses of 0, 50, 100 200, and 400 kg ha^?1 phosphorus pentoxide (P₂O₅) in randomized blocks with three replications. Phosphorus fractions were determined in soil samples collected at two depths, 0–10 and 10–20 cm, according to the methodology used by Chang and Jackson (1957 Chang, S. C. and Jackson, M. L. 1957. Fractionation of soil phosphorus. Soil Science, 84: 133–144. [Crossref] , [Google Scholar]). The inorganic P fractions presented the following sequence: P-Al > P-Fe > P-Ca. The dynamics of forms of inorganic P showed that P-Al is controlling the P bioavailability as a result of an acidic pH and a very simple and thermodynamically stable clay mineralogy, typical of very weathered and old tropical soils.     

Phosphorus Fertility Assessment of Intensively Farmed Areas of Catchments Draining to the Great Barrier Reef World Heritage Area; 2: Potential of Soils to Release Soluble Phosphorus

Abstract

The potential of fertilized cropping soils (sugarcane, vegetables, fruit trees) in river catchments that drain to the Great Barrier Reef World Heritage Area in northeastern Australia to release soluble phosphorus (P) was assessed using soil chemical tests on typical soils (0–10 cm) collected in 2003. Tests included total P, diagnostic soil P tests, estimates of P buffering, and soluble and redox sensitive soil P. Routine soil P tests proved poor predictors of CaCl₂ P (0.005 M). Values≥0.20 for the Mehlich‐3 P saturation ratio separated (P<0.01) lower from higher concentrations of CaCl₂ P. The ratio of Mehlich‐3 Fe to [Mehlich‐3 Fe+Mehlich‐3 Al] is offered as a possible simple index of redox sensitive P. Part 1 (Rayment and Bloesch 2006 Rayment, G. E. and Bloesch, P. M. 2006. Phosphorus fertility assessment of intensively farmed areas of catchments draining to the Great Barrier Reef World Heritage Area, 1: Soil phosphorus status. Communications in Soil Science and Plant Analysis, : 37 [Google Scholar]) describes the soil survey in more detail.     

Evaluation of Chemical Extractants for the Determination of Available Potassium

Abstract

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. This research was carried out to determine the potassium (K) available to corn (Zea mays) in 15 soils from the Hamedan province in the west of Iran. The treatments included two K levels [0 and 200 mg K kg^?1 as potassium sulfate (K₂So₄)] and 15 soils in a factorial experiment in a randomized block design with three replications. The results indicated that K application increased yield, K concentration, and K uptake of corn. According to the mechanism of the extraction, these extractants can be classified into four groups. The first group of extractants, acidic extractants, includes 0.02 M strontium chloride (SrCl₂)+0.05 M citric acid, 0.1 M hydrochloric acid (HCl), and Mehlich 1. The second group includes 0.1 M barium chloride (BaCl₂), 0.01 M calcium chloride (CaCl₂), and 1 M sodium acetate (NaOAc). The third group includes 1 M ammonium acetate (NH₄OAc), ammonium bicarbonate–diethylenetriamine tetraacetic acid (AB‐DTPA), and finally distilled water. The results showed that correlation between extractants in each groups were significantly high. Correlation studies showed that NH₄OAc and AB‐DTPA cannot be used as available K extractants. The correlation of other extractants with relative yield, plant response, and K uptake were significantly high. Therefore, these extracting solutions can be used as available K extractants.

Potassium critical levels by extractants were also determined using the method by Cate and Nelson (1971) Cate, R. B. and Nelson, L. A. 1971. A simple statistical procedure for partitioning soil test correlation into two classes. Soil Science Society of America Proceeding, 35: 658–660. [Crossref], [Web of Science ®] , [Google Scholar]. Potassium critical levels for 90% relative yield were 29, 27, 82, 84, 45, 145, and 272 mg kg^?1 for 0.002 M SrCl₂, distilled water, 0.02 M SrCl₂+0.05 M citric acid, 0.1 M HCl, Mehlich 1, 1 M NaOAC, and 0.1 M BaCl₂, respectively.     

Correction and standardization of critical limit of zinc for maize (Zea mays L.) crop: Bangladesh perspective

Abstract

Critical limit (CL) determination of zinc (Zn) is very important for predicting response of maize crop to its application in soils and for the crop’s actual fertilizer requirement. This study was conducted at Bangladesh Agricultural Research Institute, Gazipur, to determine the CL of Zn for maize grown in 20 soils collected from the five Agro–Ecological Zones during January to March, and April to June of 2017. The available Zn content of soils and maize biomass were estimated utilizing the extraction method with 0.005?M diethylene triamine pentaacetic acid (DTPA). During January to March and April to June 2017, the amount of DTPA extractable Zn in different soils ranged from 0.60–3.25?mg?kg^?1 and 0.50–1.68?mg?kg^?1, respectively. During both periods of crop growth (January to March and April to June, 2017), the soil available zinc was negatively significantly correlated with soil pH, available P, exchangeable Ca, exchangeable Mg and positively significantly correlated with relative dry matter (DM) yield. Soil Zn also positively significantly correlated with maize tissue Zn content (r?=?0.521*). However, the CL of Zn were estimated to be 0.84?mg kg^?1 in soils and 26.1?mg kg^?1 in maize tissue for maize cropping as determined by Cate and Nelson’s (1965 Cate, R. B., and L. A. Nelson. 1965. A rapid method for correlation of soil test analysis with plant response data. International soil testing series technical Bulletin No. I North Caroline State University, Agricultural Experiment Statistics, Releigh, USA, pp. 135–136. [Google Scholar]) graphical procedure. Maize crop may respond to Zn application in soils containing Zn at/below the above level. This data may be used for predicting plant response to Zn fertilizer and development of crop Zn nutrition guide for maximum production.     

Phosphorus Fertility Assessment of Intensively Farmed Areas of Catchments Draining to the Great Barrier Reef World Heritage Area; 1: Soil Phosphorus Status

Abstract

Australia's reef water quality protection plan has a key objective: “reduce the load of pollutants from diffuse sources in the water entering the Reef.” This article reports on a survey to assess the contemporary phosphorus (P) status of fertilized cropping soils across 21 catchments in coastal Queensland, Australia. The survey focused on surface soils from cane farms, vegetable and subtropical/tropical fruit tree sites. There were sampling depth effects on P levels in sugar and fruit tree sites (lower with depth). Importantly, 84% of 105 sugarcane sites were excessively fertile and only 3% rated low (P deficient). Some 75% of 16 vegetable sites and 38% of 8 fruit tree sites had excess ratings for extractable soil P fertility. Highest total P levels (0–10 cm) occurred in fruit tree sites, followed by vegetable and sugarcane soils. There are regional differences in P soil fertility, and the recycling of mill by‐products needs attention. Part 2 (Bloesch and Rayment 2006 Bloesch, P. M. and Rayment, G. E. 2006. “Phosphorus fertility assessment of intensively farmed areas of catchments draining to the Great Barrier Reef World Heritage Area, 2: Potential of soils to release soluble phosphorus”. In Communications in Soil Science and Plant Analysis 37 [Google Scholar]) examines the potential of these soils to release soluble P in a nutrient‐sensitive area.     

Short-Term Ion Uptake by Phalaenopsis as Affected by Concentration of the Solution

ABSTRACT

Nutrient uptake over a 72 h culture period by clonal micropropagules of Phalaenopsis Tanigawa × Yukimai Dream ‘KS 370’ and ‘KS 352’ were surveyed by Ichihashi's (1997) Ichihashi, S. 1997. “Orchid production and research in Japan”. In Orchid Biology, Reviews and Prospectives, Edited by: Arditti, J. and Pridgeon, A. M. 171–212. Dordrecht, , The Netherlands: Kluwer.  [Google Scholar] nutrient solution at the original ion strength and its half and quarter. Uptake of major anions [nitrate (NO₃ ^?), phosphate (H₂PO₄ ^?), and sulfate (SO₄ ^2?)] and cations [ammonium (NH₄ ⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺)] measured with an ion chromatograph increased as the ionic strength of the solution increased in both cultivars. The final uptake rates of nutrients were 0.8, 2.0, 2.1, 1.2, 3.0, 2.0, and 1.6 me L^?1, respectively in the order of ions mentioned above. The ratios of the uptake rates between cations (mono or bivalent) were almost in proportion to the ratio of their initial ion strength. Therefore, no antagonistical absorption of cations was found in that ion strength. Leaf content of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and copper (Cu) increased as the ionic strength of the solution increased, but concentrations of iron (Fe), manganese (Mn), and zinc (Zn) were not affected significantly. Nitrogen (N) content of leaves in ‘KS 370’ after 72 h culture increased significantly by increasing the ionic strength of the solution. Root concentrations of P, K, Ca, Mg, and Fe increased as the ionic strength of the solution increased in both cultivars. The N concentrations of roots in either ‘KS 370’ or ‘KS 352’ had positive correlations with an increasing ionic strength of the solution, although they were constantly greater in ‘KS 370’ than in ‘KS 352’. The greatest fresh weight was obtained when the plants were cultured in a half strength solution. Whereas dry weight decreased in all treatments as the ionic strength of the solution decreased. These findings show that increased ion absorption affected plant dry weight. The obtained findings provide fundamental information for the closed hydroponic system of phalaenopsis cultivation.     

Commercial Extract of Ascophyllum nodosum Improves Root Colonization of Alfalfa by Its Bacterial Symbiont Sinorhizobium meliloti

The soil bacterium Sinorhizobium meliloti forms a symbiotic relationship with alfalfa (Medicago sativa) roots, which results in the formation of intracellular root nodules. This symbiosis increases nitrogen (N) in the soil; however, to establish such a synergistic relationship, a complex communication system is required between the bacterium and its legume host. Rhizobacteria are known to respond to plant root exudates and produce signal molecules known as “Nod” factors. Research suggests that the brown seaweed (Ascophyllum nodosum) extract (ANE) stimulates both root nodulation and growth of alfalfa (Khan et al. 2011 Khan, W., Palanisamy, R., Critchley, A. T., Smith, D. L., Papadopoulos, Y. and Prithiviraj, B. 2011. Ascophyllum nodosum (brown seaweed) extract and its organic fractions stimulate root nodulation and growth of alfalfa (Medicago sativa). Communications in Soil Science and Plant Analysis (Accepted),  [Google Scholar]). To elucidate the mechanism of action, the effects of ANE on the early stages of root–rhizobia interactions were examined. A. nodosum extract (ANE) and its organic fractions were prepared and alfalfa roots were treated. After 2 days, the treated roots were inoculated with S. meliloti. The roots from treated plants were excised and observed for colony-forming units. To verify whether ANE elicited the synthesis and secretion of factors similar to those induced by luteolin, S. meliloti cultures were treated with ANE and the bacterial components were analyzed by high-pressure liquid chromatography (HPLC). To study Nod factor induction by S. meliloti due to ANE treatment, a root hair deformation assay was performed. A translational fusion of S. meliloti NodC:LacZ (strain JM57) was used to observe the effect of ANE on bacterial gene expression. When S. meliloti culture medium was supplemented with ANE, no effect on bacterial growth was observed. However, it was observed that the attachment of S. meliloti to the root hairs was improved. Similarly in vitro ANE root treatments, followed by S. meliloti inoculation, increased bacterial colonies. HPLC profiles and a root hair deformation assay suggested that ANE elicits production of compounds similar to the Nod factor, which are normally induced by the plant signaling molecule luteolin. The results suggest that ANE may contain compound(s) that promote the legume–rhizobia symbiotic relationship and plant signaling.     

Die Anwendung der Ertragskurvenberechnung nach von Boguslawski und Schneider bei der Auswertung aktueller N-Steigerungsversuchsserien

Abstract

Yield curve calculation according to von BOGUSLAWSKI and SCHNEIDER as well as the EDP calculating programme, derived from it by Horst and Heyn (1988 Horst H Heyn J 1988 Ein PC-Programm zur Errechnung von Ertragskurven nach der dritten Annäherung an das Ertragsgesetz von v. Boguslawski und Schneider LUFA Kassel, hausintern  [Google Scholar]) and later also Kowert (2001 Kowert A 2001 Erstellung eines PC-Programmes zur Ermittlung von Ertragskurven bei Düngungsversuchen Diplomarbeit FH Osnabrück, FB Agrarwissenschaften, Studiengang Landwirtschaft  [Google Scholar]), are described. With the version at hand objective and reproducible results can be calculated in a fast and user-friendly way.

This program enables an exact definition of the maximum yield and the best fertilisation required; also every yield value on the basis of a given amount of nutriment can be deduced. Thereby results of tests and series with differing variations can be offset against each other together. Like this wide research series with accordingly high significance can be evaluated. Of course other parameters can be calculated in addition to the yield, too.

This yield curve calculation is particularly suitable for the evaluation of research on N-increase. Considering Hessian research on winter wheat, winter barley, winter rye, rape seed and sugar beet as example, the effects of increasing mineral N-fertilisation on the yield, the adapted financial gross earning and the N-removal with the main product of a crop are indicated.

The N-fertilisation aiming at the greatest natural yield of the tested fruit winter wheat, winter barley, winter rye, rape seed and sugar beet, requires an amount of about 145 to 225 kg N/ha. The economical optimisation of the N fertilisation is about 30 to 40 kg/ha lower with cereals compared to about 90 kg/ha lower with rape and sugar beet.

The optimisation of the N-fertilisation as to the financial gross earning leads to a significant increase of the supply-removal-account into an uncritical range for all fruits. The amount of the N-fertilisation should not be fixed on the natural yield, but on parameters of cost-effectiveness. This leads to economical and ecological advantages.     

Agronomic Implications of the Application of Lime plus Gypsum By‐products to a Hyperdistric Acrisol from Western Spain

Abstract: A laboratory experiment involving the use of leaching columns reproducing the topmost portion of a Hyperdystric Acrisol (FAO 1998 FAO. 1998. World reference base for soil resources, Rome: FAO, ISRIC, and ISSS. (World Soil Resources Report No. 84) [Google Scholar]) or plinthic Palexerult (Soil Survey Staff 2003 Soil Survey Staff. 2003. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys, Washington, D.C.: U.S. Government Printing Office. (Agriculture Handbook No. 436) [Google Scholar]) treated in its Ap horizon with sugar foam wastes and phosphogypsum was conducted. The amendments increased the contents in exchangeable calcium (Ca) of the Ap horizon and, to a lesser extent, also that of the AB horizon. However, the contents in exchangeable magnesium (Mg) and sodium (Na) decreased as much in Ap as they did in AB; by contrast, the potassium (K) content exhibited a less marked decrease. The potassium chloride (KCl)–extractable aluminium (Al) of the Ap horizon was dramatically decreased much more than that of the AB horizon by the amendments. In the soil solution from Ap, the amendments raised the pH and decreased the Al concentration; in that from AB, however, they caused an initial pH decrease, a tendency that reversed as the gypsum was leached and eventually led to the pH exceeding that in the soil solution from control. The first few water extractions exhibited increased Mg concentration. This trend was reversed in the second leaching cycle, where the concentrations of Mg in the amended columns were lower than those in the controls. In the soil solution, the variation of the Ca and sulphate (SO₄ ^2–) concentrations was influenced by the salt‐sorption effect. The total Al content in soil solution from AB increased during the first leaching cycle and then decreased during the second. The amendments decreased the activities of Al³⁺, AlOH⁺², and Al(OH)₂ ⁺ in the Ap horizon and increased those of Al³⁺, AlSO₄ ⁺, Al(SO₄)₂ ^?, and AlF⁺² in the first leaching cycle in the AB horizon. The productivity of the Ap horizon after the treatments was assessed using a wheat crop (T. aestivum, var. ‘Jabato’) in a greenhouse.     

Evaluation of different methods for the determination of saturated hydraulic conductivity for simulation of water table depth and drainage discharge using the DRAINMOD computer simulation model

The purpose of this study was to investigate application of the DRAINMOD computer simulation model for estimation of water table depth (W) and drainage discharge (q) by using different values of saturated hydraulic conductivity (K _s) in a subsurface drainage system in Kooshkak area in Fars province. These values of K _s were obtained from the drainage system, a direct measurement of K _s calculated from drainage data (K _s1), Porchet method with saturated inverse hole (K _s2), ordinary Porchet method (K _s3) and saturated Porchet obtained using an empirical equation presented by Sepaskhah and Rezaee (K _s4) (Sepaskhah AR, Rezaee A. 1998. Hydraulic conductivity measurement for subsurface drainage system. Iran Agr Res. 17:139–150). The results indicated that saturated Porchet and saturated Porchet calculated using Equation (17) are reliable for determination of K _s because their values are close to that obtained from the direct method. Furthermore, the results indicated that W fluctuations and q are estimated properly by the DRAINMOD model, as shown by an index of agreement of 0.90–1.0 and 0.99 for W and q, respectively. However, q estimations were more accurate than W fluctuations, as shown by a mean absolute error of 0.045–0.243 and 1.73–25.44 for q and W, respectively. Using different values of K _s in the model caused tangible differences between the results, especially in W fluctuations, and showed that the model is sensitive to this parameter. Among the indirect methods of K _s determination, using the measured K _s obtained by the saturated Porchet method (K _s2) resulted in more accurate W and q. It was determined that the saturated Porchet method is more difficult and time-consuming than the ordinary Porchet method. Therefore, a relationship between these two tests has been developed in the study area [similar to the equation that was presented by Sepaskhah and Rezaee (1998 Sepaskhah, A R and Rezaee, A. 1998. Hydraulic conductivity measurement for subsurface drainage system. Iran Agr Res, 17: 139–150.  [Google Scholar])] and estimation of K _s from ordinary Porchet method can then be converted to saturated Porchet method for use in DRAINMOD model.     

Mobilization of heavy metals from river sediments of Northern Greece by complexing agents

The influence of NTA, EDTA, STPP, Triton X100, PO _inf4 ^sup3 and NO _inf3 ^sup? on the mobilization of Pb, Cd, Cu, Cr and Mn from sediments of two rivers located in Northern Greece was studied. The release caused by all examined complexing agents was higher in deionized water than either Axios or Aliakmon river water due to the lack of competition of Ca and Mg cations with the heavy metals for the studied complexing agents, and the decrease of ionic strength. From all examined agents NTA and EDTA showed the greater mobilization ability. Copper showed the greater tendency for remobilization by all examined agents, (according to the order: EDTA?NTA, Triton X1004 PO _inf4 ^sup3? > NO _inf3 ^sup3? ?STPP) while Cr and Mn the smallest following the orders: NTA, PO _inf4 ^sup3? >> NO _inf3 ^sup? , Triton X1004 EDTA, STPP and STPP > EDTA > NTA > Triton X 100 ? PO _inf4 ^sup3? NO₃, respectively. An increase in mobilization was noticed with an increase of agent concentration and time of shaking.     

Influence of acidity and competition with fish on the development of ducklings in Quebec

In Quebec, in 1984 and 1985, a number of American Black Duck (Anas rubripes) and Common Goldeneye (Bucephala clangula) ducklings were reared on two acid lakes (pH 4.8 to 5.0) and one circumneutral lake (pH 6.0) in which the brook trout (Salvelinus fontinalis) populations had been manipulated. This allowed us to determine how acidity and competition with fish affected duckling feeding and growth. Strong acidity and the presence of fish were both required before the birds' development was restricted, the Black Duck being particularly affected. This result supports hypotheses on competition between fish and some waterfowl species.     

Suitability of extractant for soil available silicon and silicon response to upland paddy grown on alkaline soils of central India

Abstract

Several silicon (Si) extractants are being employed in different countries mostly for lowland acidic soils. Present investigation was conducted to evaluate suitable extractants for upland paddy grown on alkaline soils. Available Si was extracted by using ten different extractants. Tris buffer pH 7.0 (1:10) in Inceptisols showed positively highest and significant correlation with grain yield (r?=?0.870), grain Si uptake (r?=?0.887), straw yield (r?=?0.852), and straw Si uptake (r?=?0.919). However, 0.5?M acetic acid (1:2.5) in Vertisols showed positively highest and significant correlation with grain yield (r?=?0.810), grain Si uptake (r?=?0.852), straw yield (r?=?0.850), and straw Si uptake (r?=?0.929). The application of Si @ 200?kg ha^?1 along with chemical fertilizers significantly increased yield and nutrient uptake of upland paddy on Vertisols. Tris buffer pH 7.0 (1:10) and 0.5?M acetic acid (1:2.5) were suitable extractant for Inceptisols and Vertisols, respectively based on its correlation with yield and nutrient uptake.     

Fertilizer application in aid of plantation establishment in the savanna areas of Nigeria

Fertilizer trials were conducted to stimulate tree establishment and growth in the savanna region of Nigeria. The main nutrients investigated were N, P, K and B while the tree species includedAzadirachta indica (Neem),Acacia auriculiformis, Eucalyptus spp., andPinus spp. Borate application reduced the incidence of die-back of eucalypts and it also increased height growth. There was positive response to phosphate application by all species; phosphate reduced mortality considerably in pines on some sites. Response to N fertilizer by the species varied and related to type of N fertilizer. Urea was often found injurious to pines. There was strong interaction between N and P and usually response to N was not obtained on P-deficient sites. In all the cases where it was applied, there was no response to K. On more arid sites with poorly buffered soils, mineral fertilizers alone were insufficient to produce satisfactory tree growth. Application of animal manure on such sites increased survival and growth ofAzadirachta indica, E. camaldulensis andA. auriculiformis.     

A comparison of a multilayer regional-scale acid rain assessment model (MLRAPT) with a single-layer assessment model,RAPT

This study, which is part of the 1985 Assessment on Current Damages of Acid Deposition, examines uncertainty due to treating transport processes using a single-layer model compared to a multilayer model. The Multilayer Regional Air Pollutant Transport Model, MLRAPT, was run in both modes, single layer and multilayer, using 224 sources during a 22-day period in July 1978 for the northeastern United States. Comparison between the two modes indicated that the average air concentrations were highly correlated (a correlation coefficient of 0.98). However, for wet deposition of SO₄, a correlation coefficient of 0.55 between the two predicted wet deposition fields was obtained. Results of the comparison of the two modes with the observed air concentration fields and with a limited comparison of observed wet deposition indicate that caution should be used when interpreting results of a single-layer model to develop source/receptor relationships.     

<Emphasis Type="Italic">Lophopyrum</Emphasis> Á. Löve (1980), <Emphasis Type="Italic">Thinopyrum</Emphasis> Á. Löve (1980), <Emphasis Type="Italic">Trichopyrum</Emphasis> Á. Löve (1986): one,two or three genera? A study based on the nuclear 5S DNA

Many species included in the genera Lophopyrum (Á. Löve 1980), Thinopyrum (Á. Löve 1980), and Trichopyrum (Á. Löve 1986) provide germplasm that can be used by breeders to improve commercial wheat cultivars through breeding programs. But various authors have classified them differently, placing them into one, two, three or even more genera. This lack of definition raises the question posed in the title; namely, one, two or three (or more) genera? To answer this question we created a data set of 480 5S nrDNA sequences from 15 species commonly assigned to one or more of these genera by different authors. Based upon the observed variation in DNA sequence of the 5S nrRNA gene mainly within the non-transcribed spacer region, sequences can be summarized into groups or classes of 5S nrDNA that we named unit classes. Unit classes can be assigned to different haplomes within the Triticeae tribe providing a means to study genome composition and species diversity among other ends. These results, where the species were defined on the basis of haplome composition, would then be used to test hypotheses that these species can be placed within a single genus or not. Contingent upon our analyses, we found that haplome composition does not follow the previously proposed taxonomies, based on cytogenetic data, and therefore that all 15 species investigated form one single genus.     

Distribution,abundance and biomass of benthic macroinvertebrates relative to pH and nutrients in eight lakes of Nova Scotia,Canada

The lakes investigated ranged widely in pH (3.6–6.3), total phosphorus (3.3–33.1 μg.L^-1) and calcium (0.352-6.30 mq.L^-1). Several macroinvertebrate groups especially Pelecypoda, Hirudinea and Gastropoda do not occur in lakes of low pH (<5.0). The bivalve Pisidium sp. occurred in one acidic lake (pH 5.2). Apparently, this is the lowest pH occurrence for Pisidium sp. at such low calcium levels (0.35 mg.L^-1). Macroinvertebrate richness was reduced with increased levels of acidity but nutrient availability apparently controlled macroinvertebrate abundance and biomass in the lakes.